[Tex/LaTex] Expanding macro arguments in newcommand

expansionmacros

I'd like to use datetime's \monthname as part of a command; consider this snippet of command line pdflatex use:

$ pdflatex
This is pdfTeX, Version 3.1415926-1.40.11 (TeX Live 2010)
 restricted \write18 enabled.
**\documentclass{article}
entering extended mode
LaTeX2e <2009/09/24>
Babel <v3.8l> and hyphenation patterns for english, dumylang, nohyphenation, lo
aded.

*\usepackage{datetime}
(/PATH/TO/texlive/texmf-dist/tex/latex/base/article.cls
Document Class: article 2007/10/19 v1.4h Standard LaTeX document class
(/PATH/TO/texlive/texmf-dist/tex/latex/base/size10.clo))

*\newdate{someDate}{30}{05}{2011}
(/PATH/TO/texlive/texmf-dist/tex/latex/datetime/datetime.sty
(/PATH/TO/texlive/texmf-dist/tex/latex/fmtcount/fmtcount.sty
(/PATH/TO/texlive/texmf-dist/tex/latex/base/ifthen.sty)
(/PATH/TO/texlive/texmf-dist/tex/latex/graphics/keyval.sty)
(/PATH/TO/texlive/texmf-dist/tex/latex/amsmath/amsgen.sty)
(/PATH/TO/texlive/texmf-dist/tex/latex/fmtcount/fc-english.def)
(/PATH/TO/texlive/texmf-dist/tex/latex/fmtcount/fc-USenglish.def)
No configuration file fmtcount.cfg found.
))

*\newcommand\someDateStr{\getdateday{someDate} \monthname[\getdatemonth{someDate}] \getdateyear{someDate}}

*\typeout{\someDateStr}
30 \monthname[05] 2011

*\typeout{\monthname[\getdatemonth{someDate}]}
\monthname[05]

So, it looks like in the construct \monthname[\getdatemonth{someDate}], Latex will expand only \getdatemonth{someDate}, but not the \monthname part; I'm suspecting it has something to do with the square brackets as arguments, because if I try to use edef instead, I get an error:

*\edef\someDateStr{\getdateday{someDate} \monthname[\getdatemonth{someDate}] \getdateyear{someDate}}
! Argument of \reserved@a has an extra }.
<inserted text> 
                \par 
<*> ...atemonth{someDate}] \getdateyear{someDate}}

?

So, the question is: how can I use \monthname[\getdatemonth{someDate}] as a part of a newcommand, such that it results with (in this case) "May"?

Thanks in advance for any responses,
Cheers!

Best Answer

The main problem with datetime is that it is oriented towards printing dates rather than manipulating them.

A "completely expandable" version would be

\makeatletter
\newcommand{\xnewdate}[4]{\@namedef{date@#1}{/#2/#3/#4/}}
\def\xgetdateday#1{\expandafter\expandafter\expandafter\xget@I\csname date@#1\endcsname}
\def\xgetdatemonth#1{\expandafter\expandafter\expandafter\xget@II\csname date@#1\endcsname}
\def\xgetdateyear#1{\expandafter\expandafter\expandafter\xget@III\csname date@#1\endcsname}
\def\xget@I/#1/#2/#3/{#1}
\def\xget@II/#1/#2/#3/{#2}
\def\xget@III/#1/#2/#3/{#3}
\def\xgetdatemonthname#1{%
\ifcase\number\xgetdatemonth{#1}\relax
\or January%
\or February%
\or March%
\or April%
\or May%
\or June%
\or July%
\or August%
\or September%
\or October%
\or November%
\or December%
\fi}
\makeatother

\typeout{\xgetdateday{somedate} \xgetdatemonthname{somedate} \xgetdateyear{somedate}}

Related Solutions

[Tex/LaTex] Expanding arguments before macro call

The 'classical' approach is to use \expandafter

\documentclass{article}
\begin{document}

\def\x#1#2#3#4{%
  \def\arga{#2}%
  \def\argb{#3}%
  \def\argc{#4}%
  \expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter#1%
    \expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter
      {\expandafter\expandafter\expandafter\arga\expandafter\expandafter\expandafter}%
        \expandafter\expandafter\expandafter{\expandafter\argb\expandafter}\expandafter
          {\argc}}

\def\y#1#2#3{\detokenize{#1#2#3}}

\x\y{arg1}{arg2}{arg3}

\end{document}

where we need so many of them to expand arg3 then arg2 and finally arg1. (This is what is effectively wrapped up in expl3's \exp_args:Nooo).

The rule of the number of \expandafters we need is 2ⁿ – 1, where n is how many tokens we want to expand. So for one token somewhere ahead, we need just one \expandafter in each place to be 'skipped', to expand two tokens (second one then the first one) we need three \expandafters, for three tokens (as in the current case) we need seven \expandafters, and so one. This is easiest to see if you write/print out a short second and cross off the commands as TeX would read them: you'll find everything works out.

With e-TeX available, we can use an \edef and \unexpanded:

\documentclass{article}
\begin{document}

\def\x#1#2#3#4{%
  \def\arga{#2}%
  \def\argb{#3}%
  \def\argc{#4}%
  \begingroup
    \edef\x{%
      \endgroup
      \noexpand#1
        {\unexpanded\expandafter{\arga}}%
        {\unexpanded\expandafter{\argb}}%
        {\unexpanded\expandafter{\argc}}%
    }%
  \x
}    

\def\y#1#2#3{\detokenize{#1#2#3}}

\x\y{arg1}{arg2}{arg3}

\end{document}

(You can do the same without e-TeX using a series of toks, but that gets a bit confusing so I'd not normally do it.)

The question says no expl3, but for contrast the approach using a minimium of the functions it provides would read

\documentclass{article}
\usepackage{expl3}
\begin{document}
\ExplSyntaxOn
\def\x#1#2#3#4{
  \def\arga{#2}
  \def\argb{#3}
  \def\argc{#4}
  \exp_args:Nooo#1\arga\argb\argc
}    
\ExplSyntaxOff
\def\y#1#2#3{\detokenize{#1#2#3}}

\x\y{arg1}{arg2}{arg3}

\end{document}

which is I hope a lot more readable. (I'd probably want to use \exp_args:NVVV as we are using 'value stored in a variable', but that function is not pre-defined so I've avoided it here.)

[Tex/LaTex] Expanding all arguments of a command before appending it to another macro

The easiest way to tackle this is probably to force expansion of everything using \edef, as that was we avoid needing to shuffle arguments. (\mytrdc is not expandable in any case, so we can use an assignment.) One possible approach using \edef:

\documentclass{article}

\usepackage{ltxcmds}

\newcounter{mycounter}
\setcounter{mycounter}{7}

\newcommand{\mysndc}[3]{#1 #2 #3}

\newcommand{\mycommand}{}
\makeatletter
\newcommand{\mytrdc}[1]{%
  \begingroup
  \edef\x{%
    \endgroup
    \noexpand\ltx@GlobalAppendToMacro{\noexpand\mycommand}{%
    \noexpand\mysndc{\arabic{mycounter}}{#1}{\thepage}}}%
  \x}

\makeatother
\begin{document}
x

\mytrdc{8}

\newpage
\setcounter{mycounter}{4}

\show\mycommand
\end{document}

The idea is simple: create a temporary, \edefed macro \x which contains the expanded material required plus the necessary 'set up', then execute it. Everything is done in a group so we don't mess up any other meaning of \x.

Best Answer

Related Solutions

[Tex/LaTex] Expanding arguments before macro call

[Tex/LaTex] Expanding all arguments of a command before appending it to another macro

Related Question